There is a veil of secrecy to the devices (identified here: https://meridian.allenpress.com/radiation-research/article-abstract/177/6/723/209591/Risks-of-Exposu

There is a veil of secrecy to the devices (identified here: https://meridian.allenpress.com/radiation-research/article-abstract/177/6/723/209591/Risks-of-Exposure-to-Ionizing-and-Millimeter-Wave https://meridian.allenpress.com/radiation-research/article-a...) which makes them difficult to study, however millimeter waves themselves are studied: https://ieeexplore.ieee.org/abstract/document/10590163 https://ieeexplore.ieee.org/abstract/document/10590163 While looking around I also found this handbook: https://books.google.se/books?hl=en&lr=&id=OVRFDwAAQBAJ&oi=fnd&pg=PR1&dq=safety+of+millimeter+wave+scanners&ots=of_i2hartG&sig=H56OSwtZlnVLXDqsp_gaenB6q6I&redir_esc=y#v=onepage&q=safety%20of%20millimeter%20wave%20scanners&f=false https://books.google.se/books?hl=en&lr=&id=OVRFDwAAQBAJ&oi=f... which is quite informative.